In some patients with Cushing's disease, the primary disturbance may be at the level of the hypothalamus. Since hypothalamic hormones cannot be measured in the systemic circulation, such patients will be identified by analysis of the pattern of ACTH and cortisol secretion over a 24-hour period. The diagnostic accuracy and hypothesis will be evaluated by the response to drug therapy, the outcome of the pituitary surgery and the natural history of the disease.